Mining tools generally comprise a body of a ferrous metal alloy, such as steel, having a cemented carbide insert brazed into a recess in the body. A brazing alloy for this use should ideally possess the ability to wet both the body material and the cobalt-bonded tungsten carbide (the cutting tip insert material) as well as being metallurgically compatible with these materials. A brazing alloy should also possess adequate plasticity in a temperature range from about 300.degree. C. and its melting point. Suitable brazing alloys should also have a sufficiently low solidus temperature in combination with its plasticity so that a relatively low stress braze joint is formed, hence a solidus temperature below about 900.degree. C. is preferred. In addition to the foregoing properties the braze should form a joint between the insert and the body having a shear strength exceeding 38,000 pounds per square inch at room temperature to prevent the premature failure of the brazed joint between the body and the insert.
Heretofore silver-base brazing alloys have been used in mine tools to braze the insert to the body of the mine tool. While these alloys can exhibit minimum bonding strength, sufficient plasicity and desirable brazing temperatures they are expensive and some failure of joints occurs. They are also sensitive to carbide surface chemistry. Non-silver base alloys such as copper base alloys containing 10-45% by weight of zinc, minor amounts of manganese, cobalt and silicon such as disclosed in Australian Pat. No. 503,496 do not appreciably increase the bond strength of the brazed joint. It has been found that joints produced with these alloys vary considerably in strength as a function of carbide surface chemistry. Literature indicates that both surface carbon and cobalt levels significantly effect the wetability of the carbide. It is presently common practice to try to control carbide surface chemistry with various mechanical and thermal treatments.
It is believed, therefore, that a mine tool having a ferrous metal body with an insert brazed into a recess in the body when the braze exhibits from about 15% to about 20% greater braze strength than similar tools containing a silver base braze is an unexpected advancement in the art. It has also been discovered that this alloy is relatively insensitive to carbide surface chemistry, providing a consistantly high quality braze joint.